I'm relatively new to the world of gun shooting and I've been noticing a lot of AR-15's at my range. I've been looking into piecing one together for the fun of it and had some questions. FYI I live in California. I plan to shoot .22lr most of the time but would like the option to shoot .223 if the situation arises. I've been doing some research and it looks like for a simple build I just need to put together an upper and a lower. So my questions are If I buy these two pieces and put them together will I have a functioning 22 rifle? http://www.riflegear.com/p-883-cmmg-m4-le-22-lr-evolution-upper.aspx http://www.riflegear.com/p-1388-new-frontier-lw-15-complete-polymer-lower.aspx Also I see videos like this where a guy just switches a bolt and a magazine. Would this be possible with the upper and lower combination I posted? [ame]http://www.youtube.com/watch?v=8MgzYNcVtUM&feature=related[/ame] Lastly any comments on the choice of upper and lower? I'll be upfront and say, I picked the cheapest two on the site but the reviews look ok. I'm still reading through the stickies and threads, any advice is appreciated!